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Toothless: How Do Birds Eat Without Teeth?

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Author: Janice VanCleave

 

Problem

How do birds eat without teeth?

Materials

  • Needlenosed pliers
  • 10 sunflower seeds in shell
  • 1 teaspoon (5 ml) water
  • Heavy-duty plastic bag
  • 1 teaspoon (5 ml) aquarium gravel

Procedure

  1. Use the pliers to break open the shells of 10 sunflower seeds.
  2. Separate the seeds from the shells.
  3. Discard the shells, and place the seeds in the cup.
  4. Add 1 teaspoon (5 ml) of water to the cup containing the seeds.
  5. Allow the seeds to soak for 30 minutes.
  6. Place the wet seeds in the plastic bag.
  7. Add the aquarium gravel to the plastic bag.
  8. Place the bag between the palms of your hands.
  9. Rub your hands back and forth to cause the gravel to grind against the seeds inside the bag.
  10. Observe the seeds after grinding them with the stones for one minute.

Toothless

Results

The seeds are ground into a mush by the stones.

Why?

Birds do not have teeth to grind their food, but they are able to daily digest large amounts of food to meet their high energy requirements. Birds that eat seeds have strong beaks to crush the shells and then remove the softer inner seeds. These seeds are swallowed and enter a crop (a sacklike structure in the throat of many birds) where they are stored and softened. Further softening takes place after the seeds are transferred to the stomach of the bird. The softened seeds then move on into a special organ called a gizzard that has a rough lining and strong muscles. Birds swallow small pebbles that stay in the gizzard. The muscles of the gizzard move the stones and the seeds around so that the food swallowed by the bird is ground up, or "chewed," by the stones, just as the seeds were ground by the aquarium gravel. The ground mushy seeds are at last moved to the intestine, where the nutrients are picked up by the blood and taken through the body. The constant grinding wears away small pieces of the stones, which mix with the ground mush and move into the intestines and are finally eliminated as waste from the bird's body. More stones are swallowed when older ones wear away.

Let's Explore

  1. Would the size of the pebble swallowed by the bird affect the way its gizzard will grind the food? Repeat the experiment using stones larger than aquarium gravel.
  2. Can a seed in its shell pass through a bird's digestive system without being broken? Repeat the experiment without breaking the shells open.

Show Time!

Toothless

  1. How do animals without gizzards or teeth grind their food? Some, like baleen whales, do not grind their food at all. The food is swallowed, and enters the stomach where it is slowly digested. The baleen whale is the largest animal on earth and eats some of the smallest organisms. This creature lacks teeth but has rows of bones (called baleens) hanging from the roof of its mouth. These bones act like giant strainers. The whale moves through the water with its mouth open taking in huge quantities of water. Then it closes its mouth and pushes the water out through the baleens. Tiny shrimp and plankton are caught and swallowed. Demonstrate this capturing of tiny food particles by stirring loose tea leaves in a large bowl of water. Drag a tea strainer through the water and lift it out. Water drips out, leaving bits of tea leaves on the strainer. Pictures of baleen whales can be used as part of a project display along with photographs of this experiment. A summary of how the whale catches its prey should accompany the pictures.
  2. Sparrows, finches, and grosbeaks are examples of birds that have exceptionally strong bills that are able to crack the hard shells of seeds. Find out more about the bills of different birds, and show examples of bills that are used for crushing, tearing, probing, and skimming. Display pictures of these bill types with a description of the food eaten by a bird that has each bill type.

Toothless

Check It Out!

All animals with teeth do not grind their food. Snakes catch prey with sharp teeth and swallow it whole. Check out more about animals such as alligators that use their teeth not to chew with but to hold and kill their prey.

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